Thank you for your question and you concern regarding this problem. First of all I would like to bring to your knowledge that these are very much std symptoms. If the discharge is coming directly from the urethra then there is a very high possibility that you have been transmitted with a std. as you told that you had sex 4 days ago, there is a possibility of one of the various diseases that you may be having. As you also mentioned that a sore developed on your penis then there is also a possibility that you may be having discharge from that sore. In this context there may also be a possibility that the sore got infected by the sexual intercourse. Therefore knowing details of your partner is also needed in this regard in order to know if you are suffering from any such problem. Whatever the case may be, having the possibility of std symptoms, it is highly recommended that you get a proper checkup of yourself. Through this you will know if you are facing any such problem. Almost all the std can be cured therefore there is nothing to be worried about. You just need to approach a physician for this. For future, I would also recommend you that you take the precautions while having sex. insecure sex should be avoided in order to be safe from any such disease. Using a condom is the best way to have secure sex. so take care for the future and wish you a good luck.